2. 3 Patients
We included children aged 7–15 years who were prescribed antiviral
drugs for influenza in an outpatient setting during the 2018/2019
influenza season (December 1, 2018 to March 31, 2019). During this
period, baloxavir was approved for children whose body weight was ≥10kg
without age restriction, and was available only as a tablet; we
nonetheless did not include young children in this study, assuming that
they would have had difficulty in swallowing a pill. The patients were
included into the cohort by the date of prescription (the index date),
and were followed 1–9 days after the index date; this window was
selected as comparable to those of baloxavir clinical trials [6,14].
If a patient received repeated prescriptions for antivirals after this
period ended, we regarded as the event as a separate infection and
entered the patient into the cohort again.
Underlying comorbidities conferring a high risk of influenza
complications were examined for each patient by ICD-10 code. These
included asthma or chronic lung diseases, metabolic and endocrine
disorders, neurological and neurodevelopmental disorders, heart
diseases, and blood disorders (Supplemental Materials). These
comorbidities were prespecified, harmonizing the eligibility criteria of
CAPSTONE-2 trial (a phase 3 baloxavir trial conducted exclusively in
patients at risk of severe influenza) and selected literature relevant
to complications of influenza infection [14-16]. To correctly
specify the presence of these comorbidities, patients with JMDC data
history < 12 months before the index date were excluded from
the study.